Semiconductor devices for power control, such as IGBT (Insulated Gate Bipolar Transistor), IEGT (Injection Enhanced Gate Transistor), Super junction MOSFET, Thyristor and GTO (Gate Turn Off) Thyristor and the like, are required to have small ON resistance during a switching operation in order to reduce power loss. Thus, a trench gate structure is employed in the power semiconductor devices, where a gate electrode is embedded in a trench.
In the trench gate structure, since a current channel is formed in the longitudinal direction perpendicular to a substrate, a gate interval in the lateral direction can be narrowed. As a result, it becomes possible to miniaturize a device structure and to widen a substantial channel width, whereby the ON resistance can be made smaller than that of a planar gate structure in which the current channel is formed in the lateral direction. Furthermore, it is advantageous to improve performances by raising a switching speed, since the device size can be made smaller in the trench gate structure than that in the planar gate structure.
On the other hand, if miniaturization of the device structure is proceeded with by narrowing the gate interval, avalanche breakdown is prone to occur, and a short-circuit current may increase. In order to cope with them, the ON resistance can be reduced, while a drain-source breakdown voltage is maintained, by forming a trench contact, which is electrically in contact with a base layer, between the gate electrodes. However, it requires a space where the trench contact is provided, and the miniaturization is inevitably limited.